Electrical sub-assembly

ABSTRACT

An electrical sub-assembly comprises a stator having a plurality of coils and a cooling means attached to the stator. The electrical sub-assembly further comprises a plurality of pairs of diodes attached to the cooling means, each pair of diodes being in antiparallel configuration and having three electrical terminals. One of the three electrical terminals is a common terminal shared by both diodes in each pair of diodes. A plurality of busbars electrically connect each of the diodes to at least one of the plurality of coils via one or more of the electrical terminals. In use, the cooling means is configured to simultaneously cool the stator and the plurality of diodes. The electrical sub-assembly may have particular application as a part of a switched reluctance machine.

TECHNICAL FIELD

The invention relates to an electrical sub-assembly. The inventionparticularly, but not necessarily, relates to an electrical sub-assemblyfor use in a hybrid electric vehicle or an electric vehicle.

BACKGROUND

Switched reluctance machines (SRMs) are becoming increasingly popular asvariable speed drives. Principally, this is because SRMs are simple tobuild and inexpensive, at least when compared to more commonly usedmotors. However, SRMs are underutilised for commercial applications, asthey typically exhibit high torque ripple and require non-standardasymmetric half bridge converters. FIG. 1 illustrates an embodiment of arecently proposed drive configuration 110 which allows an SRM having sixphases A, B, C, D, E, F to be driven by an standard three-phase ACinverter 120. A plurality of diodes 114 having electrical connections116 are arranged alternatively between the output phases of the powerconverter 120 to convert the bipolar current waveform output from eachphase of the three-phase converter into two unipolar half waveforms,relating to the positive and negative regions of the waveform,respectively. This enables the three-phase inverter 120 to operate as itwould for a three-phase electric machine, while supplying a six-phaseSRM and having only three power connections 122 between the inverter 120and the motor. The increased number of phases permits low torque rippleand the diode arrangement allows use of standard full bridge converters.However, further improvements to the proposed drive configuration arerequired to improve the suitably of SRMs for commercial applications,particularly hybrid electric vehicles (HEVs) and electric vehicle (EVs).

It is an object of embodiments of the invention to at least mitigate oneor more of the problems of the prior art.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided an electricalsub-assembly comprising: a stator having a plurality of coils; coolingmeans attached to the stator; and a plurality of pairs of diodesattached to the cooling means, each pair of diodes being in antiparallelconfiguration and having three electrical terminals, one of the threeelectrical terminals being a common terminal shared by both diodes ineach pair of diodes, wherein the cooling means is configured to, in use,simultaneously cool the stator and the plurality of diodes. Theinvention may advantageously enable mounting of the diodes to thecooling means. Additionally, the invention may reduce the number ofelectrical components, e.g. busbars, required to connect the driveconfiguration to the coils of the stator.

Preferably, the electrical sub-assembly further comprises a plurality ofbusbars electrically connecting each of the diodes to at least one ofthe plurality of coils via one or more of the electrical terminals.

In certain embodiments, one or more of the plurality of pairs of diodesmay each be formed as a single electrical component in which a singlepair of diodes is packaged.

In certain embodiments, one or more of the plurality of pairs of diodesmay together be formed as a single electrical component in whichmultiple pairs of diodes are packaged.

In certain embodiments, at least two of the plurality of pairs of diodesmay be electrically connected to one another by an electrical connectionwithin the single electrical component.

In certain embodiments, the common terminals of the plurality of pairsof diodes may each electrically connected to a respective one of theplurality of busbars. In certain embodiments, n pairs of diodes may beelectrically connected to 3n busbars. In certain embodiments, three ofpairs of diodes may be electrically connected to nine busbars.

In certain embodiments, two or more of the common terminals of theplurality of pairs of diodes may together be electrically connected toone of the plurality of busbars. In certain embodiments, n pairs ofdiodes may be electrically connected to 3n−1 busbars. In certainembodiments, three of pairs of diodes may be electrically connected toeight busbars. In certain embodiments, n pairs of diodes may beelectrically connected to 3n−2 busbars. In certain embodiments, three ofpairs of diodes may be electrically connected to seven busbars.

According to a further aspect of the invention, there is provided anelectrical sub-assembly comprising a stator having a plurality of coils;cooling means attached to the stator; a plurality of diodes attached tothe cooling means, each of diodes being electrically connected to arespective one of the plurality of coils; and a plurality of busbars,each busbar being electrically connected to one or more of the pluralityof diodes and/or one or more of the plurality of coils, wherein thecooling means is configured to, in use, simultaneously cool the statorand the plurality of diodes.

In certain embodiments, the plurality of diodes may comprise at leasttwelve diodes, the total number of diodes being a multiple of six.

In certain embodiments, the plurality of busbars may comprise a firstbusbar, a second busbar and a third busbar. In certain embodiments, n/3of the plurality of diodes and respective coils may electrically connectthe first and second busbars, a further n/3 of plurality of diodes andrespective coils may electrically connect the first and third busbars,and the remaining n/3 of the plurality of diodes and respective coilsmay electrically connect the second and third busbars.

In certain embodiments, the plurality of busbars further comprises afourth busbar. In certain embodiments n/3 of the plurality of diodes andrespective coils may electrically connect the first and second busbars,a further n/3 of plurality of diodes and respective coils mayelectrically connect the third and second busbars, and the remaining n/3of the plurality of diodes and respective coils may electrically connectthe fourth and second busbars.

In certain embodiments, the cooling means comprises a casing. In certainembodiments the cooling means may at least partially surrounds thestator. In certain embodiments, the cooling means may be configured toreceive a supply of cooling fluid.

According to a further aspect of the invention, there is provided anelectric machine comprising the electrical sub-assembly as describedabove.

In certain embodiments, the electric machine may be a motor, andoptionally the motor has at least six-phases. In certain embodiments,the electric machine may be a generator, and wherein optionally motorhas at least six-phases.

According to a further aspect of the invention, there is provided avehicle comprising an electric machine as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of exampleonly, with reference to the accompanying figures, in which:

FIG. 1 shows a schematic of a drive configuration for a six-phase SRMaccording to the prior art;

FIG. 2 shows a schematic of a drive configuration for a six-phase SRMaccording to an embodiment of the invention;

FIG. 3 shows a schematic of a drive configuration for a six-phase SRMaccording to a further embodiment of the invention;

FIG. 4 shows a schematic of a drive configuration for a six-phase SRMaccording to a further embodiment of the invention;

FIG. 5 shows a schematic of a drive configuration for a six-phase SRMaccording to a further embodiment of the invention;

FIG. 6 shows a schematic of a partial drive configuration for asix-phase SRM according to a further embodiment of the invention; and

FIG. 7 shows a schematic of a partial drive configuration for asix-phase SRM according to a further embodiment of the invention.

DETAILED DESCRIPTION

An electrical sub-assembly according to embodiments of the inventionwill now be described with reference to FIGS. 2 to 5. FIG. 2 shows aschematic of a drive configuration 210 for a six-phase switchedreluctance machine (SRM), specifically a switched reluctance motor,having six phases A, B, C, D, E, F. The sub-assembly comprises a statorhaving a plurality of coils 212 and a cooling means attached, e.g.mounted, to the stator. In certain embodiments, the cooling means maycomprise a cooling jacket (which may be referred to as a water jacket).The cooling means may be configured such that, in use, the cooling meanscools the stator. In certain embodiments, the cooling means may comprisea casing, a fluid inlet and a fluid outlet. The cooling means may atleast partially surround the stator and/or may be a cylindrical casing.In use, a pressurised cooling fluid, e.g. water or oil, may be suppliedto the casing through the fluid inlet to circulate through the casingbefore being discharged therefrom via the fluid outlet. Whilecirculating through the casing, the cooling fluid may absorb heat fromthe stator, thus cooling stator. In certain embodiments, the coolingmeans may comprise a Peltier cooler, i.e. a thermoelectric cooler. Incertain embodiments, the cooling means may comprise oil cooling applieddirectly to the coils 212 and the diodes 214, i.e. a flooded motor.

The electrical sub-assembly further comprises a plurality of pairs ofdiodes 214 attached, e.g. mounted, to the cooling means. In certainembodiments, the electrical sub-assembly may comprise three pairs ofdiodes 214. The diodes 214 are attached to the cooling means such that,in use, the cooling means is capable of cooling the diodes 214.Therefore, in use, the cooling means may simultaneously cool both thestator and the diodes 214. Each pair of diodes 214 is in antiparallelconfiguration, i.e. electrically connected in parallel such thatelectrical current may flow through a pair of diodes 214 in opposingdirections by flowing either in a first direction via a first diode 214in pair of diodes 214 or a second opposing direction via a second diode214 in pairs of diodes 214. Additionally, each pair of diodes 214 hasthree electrical terminals 216. Of the three electrical terminals 216 ofeach pair of diodes 214, one of the three electrical terminals 216 is acommon terminal 218 electrically connected to both diodes 214 in a pairof diodes 214, i.e. each common terminal 218 is shared by both diodes214 in a pair of diodes 214. Accordingly, two of the three electricalterminals 216 of each pair of diodes 214 may be electrically connectedto only one of the two diodes 214 in a pair of diodes 214 (although inaddition to other components in the drive configuration 210).

The electrical sub-assembly may further comprise a plurality of busbars230 electrically connecting each of the diodes 214 to at least one ofthe plurality of coils 212. The electrical connection between the diodes214 and one or more of the plurality of coils 214 is via a respectiveelectrical terminal 216. Further busbars 230 may connect a number of theplurality of coils to one another. The busbars may take the form ofconducting rings attached to the electrical sub-assembly.

The drive configuration 210 may be electrically connected to a powerconverter 220 having a plurality of output phases. In certainembodiments, the drive configuration 210 may be connected to athree-phase power converter, e.g. a full bridge converter, having threeoutput phases. Power connections 222 may electrically connect the powerconverter 220 and the drive configuration 210 to one another.Specifically, each of the power connections 222 may electrically connectto a respective one of the plurality of diodes 214. Each of the powerconnections 222 may correspond to an output phase of the converter 220,thus each of the pairs of diodes 214 may be electrically connected inline with one of the plurality of output phases of the power converter220. A first pair of diodes 214 may be associated with phases A and D ofthe SRM and may relate to a first output phase of the power converter220. A second pair of diodes 214 may be associated with phases B and Eof the SRM and may relate to a second output phase of the powerconverter 220. A third pair of diodes 214 may be associated with phasesC and F of the SRM and may relate to a third output phase of the powerconverter 220. Further busbars 230 may connect one or more of theplurality of coils to one or more of the power connections 222.

Arranged in this manner, the pairs of diodes 214 may convert a bipolarcurrent waveform output from each of the outputs phases of the powerconverter 220 into two unipolar half waveforms, each relating to apositive region and a negative region of the waveform, respectively.Consequently, the converter power converting 220 having n output phasesis able to supply a SRM having 2n phases, while having only n powerconnections 222 between the power convertor 220 and the driveconfiguration 210, where n is an integer equal to or greater than one.For example, in embodiments where power converter 220 has three outputphases, the power converter is able to supply a SRM having six phases,while having only three power connections 222 between the powerconvertor 220 and the drive configuration 222.

One or more of the plurality of pairs of diodes 214 may each be formedas a first diode unit 224, i.e. a single electrical component in which asingle pair of diodes 214 is packaged. Each of the diode units 224 maycomprise the electrical terminals 216 of the diodes 214 packagedtherein.

In certain embodiments, the drive configuration 210 may be a delta typeconfiguration, as illustrated in FIG. 2. Referring to the driveconfiguration 210 illustrated in FIG. 2, the common terminals 216 of theplurality of pairs of diodes 214 may each be electrically connected to arespective one of the plurality of busbars, i.e. for each electricalterminal 216 there is one busbar connecting the diodes 214 to the coils.For example, there may be three pairs of diodes 214, thus nineelectrical connections 216 each connected to at least one of ninebusbars, respectively. This example is possible using the driveconfiguration 210 illustrated in FIG. 2.

FIG. 3 shows a schematic of a drive configuration 310 of a furtherembodiment of the invention, with reference numerals offset by a factorof 100 identifying like features discussed above with reference to FIG.2. One or more of the plurality of pairs of diodes 314 may together beformed as a second diode unit 326, i.e. a single electrical component inwhich a multiple pairs of diodes 314 are packaged. In certainembodiments, the second diode unit 326 may comprise a plurality of firstdiode units 224 (see FIG. 2). The second diode unit 326 may comprise theelectrical terminals 316 of the pairs of diodes 314 packaged therein.

FIG. 4 shows a schematic of a drive configuration 410 of a furtherembodiment of the invention, with reference numerals offset by a factorof 200 identifying like features discussed above with reference to FIG.2. In certain embodiments, the drive configuration 410 may be a startype configuration, as illustrated in FIG. 4. Referring to driveconfiguration 410 illustrated in FIG. 4, two or more the commonterminals 416 of the plurality of pairs of diodes 414 may together beelectrically connected to one of the plurality of busbars 430, i.e. twoor more the common terminals 416 may be electrically connected to thesame busbar 430. Thus, in certain embodiments, there is at least onefewer busbars connecting the diodes 414 to the coils than the number ofelectrical connections 416. For example, there may be three pairs ofdiodes 414, thus nine electrical connections 416 connected to sevenbusbars 430, with the respective three common terminals 418 beingconnected to one busbar 430. This example is possible using the driveconfiguration 410 illustrated in FIG. 4.

FIG. 5 shows a schematic of a drive configuration 510 of a furtherembodiment of the invention, with reference numerals offset by a factorof 300 identifying like features discussed above with reference to FIG.2. As illustrated in FIG. 5, an internal electrical connection 528within the second diode unit 426 may electrically connect at least twopairs of diodes 514. Consequently, two pairs of diodes 514 may share acommon terminal 518. The internal electrical connection 528 may enabledelta type drive configurations, as illustrated in FIG. 5, to have toleast one fewer busbars 530 connecting the diodes 514 to the coils thanthe number of electrical connections 516, i.e. two or more the commonterminals 516 may be electrically connected to the same busbar 530. Forexample, there may be three pairs of diodes 514, thus nine electricalconnections 516 connected to seven busbars 530, with the two of thethree common terminals 518 being connected to one busbar 530. Thisexample is possible using the drive configuration 510 illustrated inFIG. 5. While star type drive configurations advantageously have nothird harmonic currents, delta type connections may be used in preferredembodiments of the invention to minimise diode current rating and diodesize and cost.

An electrical sub-assembly according to further embodiments of theinvention will now be described with reference to FIGS. 6 and 7. FIG. 6shows a schematic of a partial drive configuration 610 for a six-phaseswitched reluctance machine (SRM), specifically a switched reluctancemotor. The sub-assembly comprises a stator having a plurality of coils612 and a cooling means attached, e.g. mounted, to the stator. Thecooling means may be as described above. The electrical sub-assemblyfurther comprises a plurality of diodes 614 attached, e.g. mounted, tothe cooling means. Each of diodes 614 may be electrically connected to arespective one of the plurality of coils 612.

The electrical sub-assembly further comprises a plurality of busbars630, each busbar being electrically connected to one or more of theplurality of diodes 614 and/or one or more of the plurality of coils612. As above, the cooling means is configured to, in use,simultaneously cool the stator and the plurality of diodes 614.

While only two diodes 614 and their respective coils 612 are illustratedin FIG. 6, the plurality of diodes 614 may comprise any number of diodes614 greater than or equal to twelve diodes 614, as long as the totalnumber of diodes 614 is a multiple of six. Referring the driveconfiguration 610 illustrated in FIG. 6, n/3 of the plurality of diodes614 and respective coils 612 may electrically connect a first busbar 630and a second busbar 630 to one another. A further n/3 of plurality ofdiodes 614 and respective coils 612 may electrically connect a thirdbusbar 630 and the second busbar 630 to one another. The remaining n/3of the plurality of diodes 614 and respective coils 612 may electricallyconnect the fourth and second busbars. The drive configuration 610illustrated in FIG. 6 may be a star type configuration. Half of theplurality of diodes 614 and respective coils 612 connecting one busbar630 with another may allow electrical current to flow in a firstdirection, e.g. from the first busbar 630 to the second busbar 630, andthe remaining half may allow electrical current to flow in a secondopposing direction, e.g. from the second busbar 630 to first busbar 630.

FIG. 7 shows a schematic of a partial drive configuration 710 of afurther embodiment of the invention, with reference numerals offset by afactor of 100 identifying like features discussed above with referenceto FIG. 6. While only two diodes 714 and their respective coils 712 areillustrated in FIG. 7, the plurality of diodes 714 may comprise anynumber of diodes 714 greater than or equal to twelve diodes, as long asthe total number of diodes 714 is a multiple of six. Referring the driveconfiguration 710 illustrated in FIG. 7, n/3 of the plurality of diodes714 and respective coils 715 electrically may connect a first busbar 730and a second busbar 730 to one another, where n is a integer equal to orgreater than twelve and is a multiple of six. A further n/3 of pluralityof diodes 714 and respective coils 712 may electrically connect thefirst busbar 730 and a third busbar 730 to one another. The remainingn/3 of the plurality of diodes 714 and respective coils 712 mayelectrically connect the second busbar 730 and the third busbar 730 toone another. The drive configuration 610 illustrated in FIG. 7 may be adelta type configuration. As above, Half of the plurality of diodes 714and respective coils 712 connecting one busbar 730 with another mayallow electrical current to flow in a first direction, e.g. from thefirst busbar 730 to the second busbar 730, and the remaining half mayallow electrical current to flow in a second opposing direction, e.g.from the second busbar 730 to the first busbar 730.

In certain embodiments, the electrical sub-assembly has particularapplication in a traction motor for use in a vehicle, for example ahybrid electric vehicle (HEV) or an electric vehicle (EV). Certainembodiments of the invention enable mounting of the diodes to thecooling means. Certain embodiments of the invention reduce the number ofelectrical components, e.g. busbars, required to connect the driveconfiguration to the coils of the stator.

All of the features disclosed in this specification (including anyaccompanying claims and drawings), and/or all of the steps of any methodor process so disclosed, may be combined in any combination, exceptcombinations where at least some of such features and/or steps aremutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims and drawings), may be replaced by alternative features servingthe same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of any foregoingembodiments. The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed. The claims should not be construed to cover merely theforegoing embodiments, but also any embodiments which fall within thescope of the claims.

The invention claimed is:
 1. An electrical sub-assembly comprising: a stator having a plurality of coils; a plurality of pairs of diodes, each pair of diodes being in antiparallel configuration and having three electrical terminals, one of the three electrical terminals being a common terminal shared by both diodes in each pair of diodes; and a plurality of busbars electrically connecting each of the diodes to at least one of the plurality of coils via one or more of the electrical terminals.
 2. An electrical sub-assembly according to claim 1, wherein one or more of the plurality of pairs of diodes are each formed as a single electrical component in which a single pair of diodes is packaged.
 3. An electrical sub-assembly according to claim 1, wherein one or more of the plurality of pairs of diodes are together formed as a single electrical component in which multiple pairs of diodes are packaged.
 4. An electrical sub-assembly according to claim 3, wherein at least two of the plurality of pairs of diodes are electrically connected to one another by an electrical connection within the single electrical component.
 5. An electrical sub-assembly according to claim 1, wherein the common terminals of the plurality of pairs of diodes are each electrically connected to a respective one of the plurality of busbars.
 6. An electrical sub-assembly according to claim 5, wherein n pairs of diodes are electrically connected to 3n busbars.
 7. An electrical sub-assembly according to claim 1, wherein two or more of the common terminals of the plurality of pairs of diodes are together electrically connected to one of the plurality of busbars.
 8. An electrical sub-assembly according to claim 7, wherein n pairs of diodes are electrically connected to 3n−1 busbars.
 9. An electrical sub-assembly according to claim 7, wherein n pairs of diodes are electrically connected to 3n−2 busbars.
 10. An electrical sub-assembly according to claim 1, wherein the cooling means at least partially surrounds the stator.
 11. An electric machine comprising the electrical sub-assembly according to claim
 1. 12. A vehicle comprising an electric machine according to claim
 11. 13. An electrical sub-assembly according to claim 1, further comprising a cooling means attached to the stator, wherein the plurality of pairs of diodes are attached to the stator and the cooling means is configured to, in use, simultaneously cool the stator and the plurality of diodes. 